Periodic wave repeater



Aug. zo, 1940.

H. A, WHEELER' ET AL PERIODIC WAVE REPEATER Filed Oct. 21, 1938 FIG.l.

SYNOHRONIZING SOURCE SYNGHRONIZING SOURCE WHEELER ILS ATTORNEY Patented Aug'. 1940 PATENT OFFICE PERIODIC WAVE REPEATER Harold 'A. Wheeler, Great Neck, and John C. Wilson, Bayside, Long Island, N. Y., assignors n`to Hazeltine Corporation, a corporation of Delaware Application'october 21, 1938, Serial No. 236,200

11 Claims.

This invention relates to periodic-wave repeaters and, while the invention is of general application, the repeater of the invention is particularly suitable for deriving from a given wave a wave of submultiple frequency for use as a timing wave in a television-signal transmitter. The invention is also of particular utility in oscillators for generating periodic pulses which are precisely timed by means of a delay network, the

) timing of whichdoes not depend primarily on the materials utilized in the timing circuit. A further embodiment of particular utility comprises the selection of synchronizing pulses for a television receiver out of other disturbances such 5 as static.

In generating timing pulses in a modulatedcarrier television-signal transmitter, some of which form component parts of the transmitted signal, it is customary to generate high-frequency D waves which are stabilized with respect to the source of alternating current at the transmitter and to derive therefrom waves of submultiple frequencies. The submultiple frequency waves so developed are used for the Various timing op- 5 erations necessary to generate and transmit the composite television signal. For example, in developing and transmitting a television signal involving double-interlaced scanning and 441 lines per frame, it is customary to develop a high-fre- D quency wave, for example, of 26,460 cycles, 'which is frequency-stabilized with respect to a source of E50-cycle power supplying the transmitter. From this high-frequency wave there is derived a submultiple-frequency wave of 13,230 cycles, that is,

5 half the frequency of the high-frequency wave,

which is utilized to produce line-frequency synchronizing pulses for the transmitted signal. By a further series of subdivisions, a 60-cycle Wave is developed and is utilized to provide eld-frequency pulses for the transmitted signal.

A high degree of precision is essential in the relation between the frequencies of the diierent wave generators which go to make up the timer chain of the system. For this reason, it is customary to develop the waves in the manner described above rather than to generate waves of increasingly higher frequencies from .the lowfrequency source supplying the transmitter. However, in subdividing a generated high-fre- 0 quency wave to derive the waves of lower frequency, it is difcult to secure submultiple generators or frequency dividers for each of the steps which are not subject to some operating uncer- `|5 tainties. If a particular wave generator of low- (Cl. Z50-36) er frequency is to produce pulses ofa frequency alternately charged from a direct-current source and discharged, one of the operations being controlled by a vacuum tube. In this type of circuit, the active period of the tube depends not only upon the control Wave, usually applied to the control grid, but also upon the volta-ge of the condenser which is effectively coupled into the anode circuit of the tube and, therefore, effects its anode voltage. In many circuits of this type the condenser is charged relatively slowly, either linearly or exponentially, and discharged rapidly, or vice versa. As a result, the anode voltage varies by a substantial amount during the initial portion of the linear or exponential charge or discharge and the slope of the anode voltage wave during the nal portion of this period is of relatively low value, so that the control tube may be controlled by a Wrong pulse in the controlling Wave or by some extraneous iniiuence. That is, such a system is much too sensitive to controlling eiects on its control electrode during a substantial portion of the linear or exponential charging or discharging period.

In television receivers it is diicult in some instances to select synchronizing pulses out of other disturbances, such as static. It is highly desirable, therefore, to provide a selecting means for the purpose which is insensitive or blocked against operation by such extraneous influences except during a short interval in which it is desired to select a particular pulse.

stable electrical parameter for the reason that it is dependent largely on materials, temperature, etc. It is highlydesirable, therefore, to provide an oscillator having a feed-back circuit the timing of which depends on more stable electrical parameters. Capacitance and inductance are stable electrical quantities'because they depend mainly on space dimensions rather than materials.

A concentrated resonant circuit made of capacitance and inductance has undesired inertia or ywheel eiect. This objection is overcome by dividing the capacitance and inductance along a transmission'line or among `the sections of a wave filter, either forming a delay network. The network is made aperiodic by resista-nce termination matching its image impedance, whereby the flywheel effect is destroyed while retaining the advantage of timing by stable electrical quantitles.

It is an object of the invention, therefore, to provide a periodic-wave repeater in which the time constant of the timing circuit depends on stable electrical quantities.

It is a further object of the invention to provide a periodic-wave repeater in which the period thereof is dependent on an electrical delay network as distinguished from a concentrated resonant-circuit or time-constant circuit.

It is a further object of the invention to provide an improved periodic-wave repeater, the operation and period of which are determined by predetermined pulses whichmay be selected out of disturbances such as "static.

It is a further object of the invention to pro- Viride a submultiple generator or frequency divider which is rendered completely inoperative except at predetermined' Yintervals determined by a delay network, the timing of which depends mainly on stable capacitance and inductance as distinguished from unstable resistance.

In accordance with the invention, a periodicwave repeater comprises a vacuum tube having sensitivity-determining and output circuits and feed-back means between the sensitivity-determining and output circuits having a time constant determined by an electrical delay network.

As used in this specication, the term delay network is defined as one in which the time delay of an instantaneous sharp pulse transmitted through the network is at least twice as great as the broadening of the pulse by the network, the time delay being measured as the time interval between the transmitted pulse in the input circuit and the peak of the pulse in the output circuit of the network, and the broadening eiect being measured as the time duration of the output pulse at about half of peak amplitude, caused by its transmission through the network. In a wave filter, this means that several sections are necessary. Further, as used herein, the word pulse refers to an electrical wave having a wave formI characterized by a steep leading portion or a steep trailing portion, or both, the amplitude of which approximates the amplitude of the wave, and the duration of which is an inappreciable fraction of the duration of the wave.

An input circuit or sensitivity-determining circuit of the tube is controlled normally to maintain the tube in a weak or inoperative condition and the delay network between the input and output circuits is adapted to supply a sensitizing pulse to the input, circuit of the tube to condition,

the tube for operation at a predetermined time interval after the next previous occurrence of a pulse in the output circuit.

In accordance with a preferred embodiment of the invention, synchronizing pulses are also applied to the input circuit of the wave generator and the time at which the generator is triggered is dependent upon the joint occurrence of a synchronizing pulse and a pulse fed back by the delay network. In the absence of either of these two pulses, therefore, the generator fails 'to operate.

In a modified form of the invention, the synchronizing circuit may be omitted and the period of the oscillator may be controlled solely by the precisely timed pulses which are fed back to the input circuit of the oscillator from the delay network, in which case the input circuit is designed to condition the tube for operation and thereby to trigger the generator on the occurrence of a single pulse.

For a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

In the drawing, Figs. 1, 3 and 5 are circuit diagrams of different embodiments of the invention while Figs. 2, 4 and 6 illustrate certain operating characteristics of the circuits of Figs. 1, 3 and 5, respectively.

Referring now more particularly to the drawing, in Fig. 1 there is shown a relaxation oscillator which is timed by a pulse transmitted in one direction through a line or filter networkv Aoperating as a delay network. The relaxation oscillator comprises a high-vacuum tube I0 connected to discharge periodically and abruptly a condenser II which is slowly charged in the meantime from a direct-current circuit comprising a battery I2 and a resistor I3. Vacuum tube III has a control grid which is normally biased partially or completely to cutoff by a battery I4 through a resistor I5. Thus, the vacuum tube under control of its grid bias normally has a relatively low or even zero repeating sensitivity. In order that the circuit of Fig. 1 comprising the high-vacuum tube I0 may operate as a conventional relaxation oscillator, there is provided a feed-back coupling comprising an inductor I6 in the output circuit of tube I0 inductively coupled to an inductor I'I in the input circuit thereof. It will be understood that the feed-back circuit including inductors I6 and II may be omitted from the circuit in case a vapor or gaseous electron-discharge tube of Thyratron type is utilized. synchronizing signals may be applied to the input circuit of vacuum tube Ill from a suitable source I8. A feed-back circuit comprising a delay network 24 is included between the output and input circuits of the wave generator. This delay vnetwork may be a smooth uniform transmission line or a smooth artificial line or a lter composed of lumped reactance elements and is shown as a simple uniform transmission line of unbalanced form having input terminals I9 and output terminals The transmission line is terminated in its image impedance at one or both of its pairs of terminals by means of resistors 2| and 22. The end I9 is connected in the cathode circuit of vacuum tube I0 while the end 20 is included in the input circuit of tube I0 in series with the source of synchronizing signals I8.

Reference is made to Fig. 2 for an explanation of the operation of the circuit of Fig. 1. Curve 2a represents a synchronizing signal having one or several pulses per cycle, three being shown, for example. In case the synchronizing signal of curve 2a. is utilized, the device operates as a. frequency divider by synchronizing at a submultiple frequency. Curve 2b shows the starting pulse of plate current which may be initiated by decreasing the negative grid bias of battery I4 during the occurrence of a synchronizing pulse. This pulse is built up by the feedback through inductors I6, I1 of therelaxation oscillator, and is quickly chopped offby the charging of condenser II. The pulse of cathode current at terminals I9 at the input end of the transmission line 24 causes a voltage pulse of positive polarity to travel along the line toward terminals 20. Curve 2c shows the later arrival of the pulse of curve 2b at the output end of the line, terminals 20, from which it is applied as a sensitizing pulse to the grid circuit of tube I0. Curve Zd shows the resultant of curve 2a, curve 2b, and curve 2c, and is the wave form of the resultant voltage applied to the grid of vacuum tube I0. If the feedback is suilicient, even if the grid bias from battery I4 is insufficient, the grid condenser and leak develop a suiiicient negative bias so that only the peaks of the wave of curve 2d cause plate current to flow, as indicated in curve 2e. These pulses of plate current are then a clean succession of pulses at the frequency determined by the desired synchronizing pulses. VIt will be understood that the firing of the oscillator is determined precisely by the instant at which the pulses of both waves 2a and 2d occur in the input circuit of vacuum tube I0. Thus it will be seen that vacuumtube I0 has a relatively low repeating sensitivity or is inoperative over the greater portion of the cycle Aand is conditioned for operation, or caused to have a relatively high repeating sensitivity, by the senstizing pulses applied from the delay network 24, in each instance at the time of the occurrence of the desired synchronizing pulse in the input circuit of the wave generator, thereby rendering the periodic-wave generator absolutely insensitive to undesired controlling influences until the time it is desired to eect operation by a selected synchronizing pulse. It will also be understood that the source of synchronizing signals I8 may be omitted, in which case the periodicity of the wave generator of Fig. 1 is controlled solely by the constants of line 24. f

In most cases, only one end of the line need be terminated, so only one of the resistors 2l and 22 is required.

The eriodic-wave generator of Fig. 3 is essentially similar to that of Fig. 1 and similar circuit elements have been given identical reference numerals. The circuit of Fig. 3 differs from that of Fig. 1 primarily in that the delay network 24 of Fig. l, which is included in the cathode circuit of the oscillator tube, is replaced by a delay network comprising low-pass filter 34 in the circuit of Fig. 3. The input pair of terminals, comprising terminals 29, of network 34 areterminated in resistance equal to the image impedance, represented by a resistor 3l and are coupled in series with condenser I I in the output circuit of vacuum tube Il). Output terminals 29' are provided for network 34. Network 34 is terminated at terminals 3U in an impedance, shown as variable resistor 3l', much less than its image impedance so as to reect a pulse of opposite polarity back to the output terminals 29', the reected pulse,

having an amplitude dependent upon the value of resistor 3|' and a delayvequal to twice that of the delay network 34 between terminals 29' and 30 plus the delay between terminals 29 and 29' in a manner similar to that described in the copending application of J. C. Wilson, Serial No. 226,875, filed August 26, 1938. The reflected pulse across terminals 29 is coupled into the input circuit of tube I0 in series with the source of synchronizing` signals I8.

Reference is made to Fig. 4 for an explanation of the operation cf the circuit of Fig. 3, insofar as it diiers from Fig. 1. Curve 4a shows the negative pulse which is applied to the network 34 from the anode circuit of vacuum tube I0; there are two output pulses shown by curve 4b, the latter of which occurs after a delay of one period as described above. It is immaterial, in the usual case, as to how much the intermediate pulse is delayed. In Fig'. 4b it has been timed to coincide with the last spurious synchronizing pulse of curve 2d so as to lessen the probability of this spurious pulse tripping the oscillator. economy in the total length of the delay network the intermediate pulse should occur just after For the beginning of Athe period. In this way the part of the line which is traversed only once by the desired reflected wave is minimized. This intermediate pulse does not produce any plate current so it does not appear in the other curves of Fig. .4. The pulse of curve 4b triggers the relaxation oscillator which impressesv another negative pulsemon the network 34 from the anode circuit, as shown by curve 4c. Curve 4d shows the resultant wave form of the voltage across the input terminals of the network 34 or the pulses of plate current representing the output of the relaxation oscillator. The representation of the various pulses at the beginning of each oscillation is not precise because they are affected by the amplitude relations, the curves of Fig. 4 merely serving to give a picture of the mode of operation.

The amplitude of the feed-back pulse of the circuit of Fig. 3 is controlled by adjusting thev value of resistor 3l'. The reflected pulse is greatest when this resistance is zero, ornwhen nizing pulses, if applied, will control the precise timing of the oscillations if the synchronizing pulses occur at such'time as to be superimposed on the delayed positive pulses from the delay network in the same manner described in more ldetail in the explanation with reference to the circuit of Fig. 1.

It will also be understood that the feedback circuit comprising inductances I6 and I'I-can Ibe omitted in the circuits of Figs. 1 and 3 and that the vacuum tube II! in such case acts merely as a repeater for the signals applied to its input circuit.

Fig. 5 is a circuit diagram of a periodic-wave generator in which feedback from the output circuit to the input circuit of the oscillator tube is provided only through a delay network so the oscillator fails to operate in the absence of the delay network. Elements which are similar to those of the circuit of Fig. 1 have been given identical reference numerals. The circuit comprises a delay network 44 having input terminals 39 and output terminals 40 properly terminated -to prevent multiple reflection by means of one or both of resistors 4| and 42, respectively.

Reference is made to Fig. 6 for an explanation of the operation of the circuit of Fig. 5. Curve 6a represents a negative voltage step applied to the input terminals of the line by closing the anode circuit of the oscillator. The negative voltage step of curve 6a is delayed through the network 44 and applied to the grid of tube I0 as a delayed step shown by curve 6b. This produces a second voltage step which is positive as applied to the line from the anode circuit, as shown in curve 6c. 'Ihis process of repeated delay and reversal produces a further succession of steps represented by curves 6d to 6g. The resultant of these steps is a succession of negative pulses of rectangular wave form in the input and output circuits of tube l0. Curve 6h shows the negative pulses of anode voltage of rectangular wave form while curve i shows the corresponding negative pulses of grid voltage.

The period of oscillation of the generator is twice the delay of the network 44. In this respect, the operation of the circuit of Fig. 5 is somewhat similar to that of Fig. 3. In the case of the circuit of Fig. 5, however, the pulse travels through the line twice in the same direction within a single cycle, instead of traversing a portion of the line once and being reected back, as in the case of the circuit of Fig. 3.

It will be understood that the control-electrode coupling condenser in Figs. 1 and 3, together with vresistor l5 may be utilized as the time-constant circuit of the repeaters in place of condenser l l and resistor I3 in a. manner well understood in the art. Theoretically the operation of the system is affected by both the time constant of the grid-cathode circuit and that of the anodecathode circuit. In practice, however, it is customary to make one of the time constantsthe controlling factor and the other so great as to leave little eiect on the operation of the system.

While there have been described what are considered to be the preferred embodiments of this invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modications as fall Within the true spirit and scope of the invention.

What is claimed is:

1. A periodic-wave repeater for producing periodic output pulses comprising, a vacuum-tube repeater stage including input and output circuits one of which comprises a sensitivity-controlling circuit, means included in said repeater stage for imparting thereto a relatively low repeating sensitivity in the absence of a sensitizing pulse applied thereto and a relatively high repeating sensitivity in the presence of a sensitizing pulse, a delay network having a time delay approximately equal to the period of the output pulses, means for applying to said delay network an input pulse occurring at the time a given output pulse of said repeater is due, and means including said network for applying to said sensitivity-controlling circuit, in response to said input pulse to said network, a sensitizing pulse delayed by said time delay and having such polarity as to sensitize said vacuum tube for operation at the time the succeeding output pulse from said repeater is due.

2. A periodic-wave repeater for producing periodic output pulses`\comprising, a vacuum-tube repeater stage including input and output circuits one of which comprises a sensitivity-controlling circuit, means included in said repeater stage for imparting thereto a relatively low repeating sensitivity in the absence of a sensitizing pulse applied thereto and a relatively high repeating sensitivity in the presence of a sensitizing pulse, a delay network having a time delay approximately equal to an integral multiple of the period of said output pulses, means for applying to said delay network an input pulse occurring at the time a given output pulse of said repeater is due, and means including said network for applying to said sensitivity-controlling circuit in response to said input pulse to said network a pulse delayed by said time delay and having such polarity as to sensitize said vacuum tube for operation at the time the succeeding output pulse from said repeater is due.

3. A periodic-wave repeater for producing periodic output pulses comprising, an output circuit and an input circuit which comprises a vacuumtube repeater stage including an output circuit and an input circuit which comprises a sensitiv` ity-controlling circuit, means included in said repeater stage for imparting thereto a relatively low repeating sensitivity in the absence of a sensitizing pulse applied thereto and a relatively high repeating sensitivity in the presence of a sensitizing pulse, a delay network having a time delay approximately equal to an integral multiple of the period of said output pulses, means for applying to said delay network an input pulse occurring at the time a given output pulse of said repeater is due, and means including said network for applying to said sensitivity-controlling circuit, in response to each input pulse to said network, a pulse delayed by said time delay and having such polarity as to sensitize said vacuum tube for operation at the time a later output puls from said-repeater is due.

4. A periodic-Wave repeater for producing periodic output pulses comprising, a vacuum-tube repeater having a sensitivity-controlling circuit and an output circuit, a delay network having a time delay approximately equal to the period of said output pulses, means for applying to said delay network an input pulse occurring at the time a given output pulse of said repeater is due to develop a delayed sensitizing pulse occurring substantially at the time a later output pulse is due, and means including said network coupled between said output circuit and said sensitivitycontrolling circuit for biasing said vacuum tube substantially to cut off to desensitize said vacuum tube for operation after each output pulse until said delayed sensitizing pulse is applied to said sensitivity-'controlling circuit.

5. A periodic-Wave repeater for producing periodic output pulses in response to periodic input synchronizing pulses comprising, a vacuum-tube repeater having a sensitivity-controlling circuit and an output circuit, means for applying to one of said circuits said synchronizing pulses, a delay network having a time delay approximately equal to the period of the output pulses, means for applying a pulse from said output circuit to said delay network, means including said network for applying to said sensitivity-controlling circuit, in response to said applied pulse to said network, a sensitizing pulse delayed by said time delay to increase the sensitivity f said vacuum tube substantially at the time when a succeeding output pulse from said repeater is due, and means for biasing said vacuum tube substantially to cut off to desensitize said vacuum tube for operation after each input synchronizing pulse to said repeater until the corresponding delayed sensitizing pulse is applied to said sensitivity-controlling circuit through said delay network.

6. A periodic-wave generator for producing periodic output pulses in synchronism with input pulses thereto comprising, a vacuum-tube repeater stage having a sensitivity-controlling circuit and an output circuit, means included in said repeater stage for impartingthereto a relatively low repeating sensitivity in the absence of a sensitizing pulse applied thereto and a relatively high repeating sensitivity in the presence of a sensitizing pulse, a delay network having a time delay approximately equal to the period of said output pulses, means for applying to said delay network a pulse occurring at the time a given output pulse of said repeater is due, and means including said network for applying to said sensitivity-controlling circuit, in response to said pulse applied to said network, a voltage including v a pulse delayed by said time delay for sensitizing said vacuum tube for operation by each delayed pulse from said network at the time the succeeding pulse from said generator is due.

7. A periodic-wave repeater for producing periodic output pulses in synchronism with input pulses thereto comprising, a vacuum-tube repeater stage having a sensitivity-controlling circuit and an output circuit, means included in said4 repeater stage for imparting thereto a relatively low repeating sensitivity in the absence of a sensitizing pulse applied thereto and a relatively high repeating sensitivity in the presence of a sensitizing pulse, a delay network having a-time delay substantially equal to the period of said input pulses, means for applying to said delay network a pulse occurring at the time a given output pulse of said repeater is due, and means including said network for applying to said sensitivity-controlling circuit, in response to said pulse applied to said network, a. voltage including a sensitizing pulse delayed with said time delay for sensitizing said vacuum tube for operation by each delayed pulse from said delay network at the time the succeeding input pulse to said repeater is due.

8. A periodic-wave repeater for producing periodic output pulses in synchronization with predetermined ones of synchronizing pulses applied thereto comprising, a vacuum-tube repeater normally biased substantially to cut off and having a sensitivity-controlling circuit and an output circuit, means for applying to one of said circuits said synchronizing pulses, a delay network having a time delay substantially equal to the period of said predetermined ones of said synchronizing pulses, means for applying to said time-delay network an input pulse occurring at the time an output pulse of said repeater is due, and means including said network for applying to said sensitivity-controlling circuit, in response to said input pulses to said network, a pulse delayed by said time delay for sensitizing said vacuum tube for operation by each delayedpulse from said delay network at the time the succeeding output pulse from said generator is due.

9. A periodic-wave repeater for producing periodic output pulses comprising, a vacuum tube having an output circuit and a sensitivity-controlling circuit, a delay network having a time delay approximately equal to the period of the output pulses, said network being a low-pass lter having a plurality of sections, whereby its time delay is much greater than its widening effect, means for applying to said delay network an input pulse occurring at the time a given output pulse of said repeater is due, a resistance termination substantially preventing reflection at one end of said lter, and coupling means including said network for coupling said output circuit to said sensitivity-controlling circuit with such polarity as to sensitize said vacuum tube for operation by each output pulse from said delay network at the time the succeeding output pulse from said repeater is due.

10. A periodic-wave repeater for producing periodic output pulses comprising, a vacuum tube having a sensitivity-controlling circuit and an output circuit, a delay network having a .time delay approximately equal to the period of the output pulses, said network comprising a lowpass filter having a plurality of sections for providing time delay much greater than its widening effect, a resistance termination substantially preventing reiiection at one end of said filter, a mismatched termination at the other end of said lter for causing Ithe desired pulse to traverse twice the part of said lter adjacent said other end, and means including said network for coupling said output circuit to said sensitivitycontrolling circuit with such polarity as to sensitize said vacuum tube by each output pulse from said network at the time the succeeding output pulse from said repeater is due.

11. A periodic-wave repeater for producing periodic output pulses comprising, a vacuum tube havingan output circuit and an input circuit adapted for negative-bias control of its'sensitivity, means including a delay network coupling said output circuit to said input circuit, said network comprising a multi-section low-pass filter with a pair of terminals at each end and an intermediate pair of terminals, a resistance less than its image impedance connected with one of said end pairs of terminals to provide a voltagereversing reflecting termination, the other two pairs of said terminals being connected, respectively, in said input and output circuits, and a resistance matching the image impedance of said iilter at one of said other pairs of terminals to provide a non-reilecting termination, rwhereby each negative output pulse oi' said vacuum tube is delayed and reversed in said network and appears as a positive pulse in said input circuit for sensitizing said repeater.

HAROLD A. WHEELER. JOHN C. WILSON. 

